1. Field of the Invention
The present invention relates to an image processing apparatus capable of performing a 3D display of a printed material, as well as relates to an image processing method.
2. Description of the Related Art
Various image processing apparatuses have been proposed that have the function of displaying the finished state of a printed material on a display device, such as a display, so as to allow previewing the finished state of printed material. Herein, the finished state of the printed material may be previewed with the aim of confirming the colors of the printed material, or confirming additional information of an output device (a printer), or confirming what is called the texture of the printing paper. Moreover, because of the function that allows previewing the finished state of a printed material, the actual state of the printed material can be presented to the user in an easy-to-understand manner. Hence, such a function helps in preventing a mismatch in the perception related to the finished state of the printed material or preventing printing errors, and thus offers an advantage of enabling achieving reduction in unnecessary tasks.
As a function that allows previewing a printed material; what is called a 3D (three-dimensional) display preview function has also been proposed that allows previewing the printed material by varying the position of lighting or the viewpoint position. Particularly, in the case of performing color reproduction by taking into account the effect of regular reflection light or the gloss of the printed material surface, or in the case of attempting to reproduce the gloss feel or the texture of the real printed material; it is effective to implement the 3D display preview function that enables varying the position of lighting or the viewpoint position.
For example, Japanese Laid-open Patent Publication No. 2012-44421 discloses a technology of simulating a 3D display preview (soft proof) by also taking into account the gloss component (i.e., the reflection of lighting). According to that technology, at the time of performing a 3D display preview, the lighting environment for viewing of the users is easily obtained and incorporated in the soft proof processing. As a result, an image of the printed material under the lighting environment for viewing is reproduced on a monitor with a high degree of accuracy.
Japanese Laid-open Patent Publication No. 2010-246049 discloses a technology in which, even in the case when a display device (display) not having a large dynamic range is used, in order to reproduce the gloss while maintaining the reproducibility of the colors of objects at the time of performing a 3D display preview; the specular colors are compressed so as to fit them within the dynamic range of the display device, the image synthesis ratio between the specular colors of objects and the diffuse reflection colors of objects is determined, and the reflected colors of objects are determined by synthesizing the specular colors of objects and the diffuse reflection colors of objects according to the image synthesis ratio that is determined.
Japanese Laid-open Patent Publication No. 2010-152533 discloses a technology in which, at the of performing a 3D display preview, in order to display on the display an image which has an identical texture to the texture of the printing surface of the printed material, a texture profile is provided that represents the correspondence relationship between a value of print data and a value of texture information data representing the texture of the printing surface.
In the technology disclosed in Japanese Laid-open Patent Publication No. 2012-44421, a single set of “lighting image data” is used at the time of performing a preview, and this single set of “lighting image data” is applied to a paper portion (a toner non-attachment portion) as well as to an image portion (a toner attachment portion). However, in such a configuration, the scope of lighting (the extent of blurring of lighting) that is reflected in a print image is same in the paper portion and the image portion. In contrast, in the actual printed material, generally, the gloss feel of the paper portion does not match with the gloss feel of the image portion. That is because the surface structure of the paper sheet is different than the surface structure of the portion of the paper sheet in which the toner is attached. Thus, in the technology disclosed in Japanese Laid-open Patent publication No. 2012-44421, with regard to a phenomenon that the scope of lighting reflected in the paper portion is different than the scope of lighting reflected in the image portion, it is not possible to express the texture (the gloss feel) of the printed material. That is, it is not possible to express the real feel of the printed material.
Moreover, from among various imaging methods, when particularly the electrophotographic image method is implemented to perform image processing and to form images, a typical phenomenon is observed in which the gloss in the medium concentration area decreases to a lower level than the paper portion and the image portion (the solid portion), and the reflection of lighting spreads widely. In such a state too, in the technology disclosed in Japanese Laid-open Patent Publication No. 2012-44421, it is not possible to reproduce colors because of the same reason as explained above.
Furthermore, in the technology disclosed in Japanese Laid-open Patent Publication No. 2012-44421, the configuration is such that a sample printed material is output and, for each of a plurality of colors, the gloss component as well as the diffuse component is obtained in advance. However, it means that an enormous number of man-hours are put into performing the measurement related to obtaining the gloss component and the diffuse component (as far as the unmeasured colors are concerned; even if derivation is done by means of interpolation, it is necessary to have a sufficient measurement result that enables estimation of all colors at a certain accuracy). Moreover, at the time of performing a preview, a look up table (LUT) is used to derive both components of the required colors. However, not only the LUT is configured to hold the characteristic values on a color-by-color basis, but also the colors have the three-dimensional degree of freedom. As a result, there is an enormous volume of data present in the LUT. Moreover, during the process of referring to the LUT and deriving both components of the required colors, an enormous calculation load is also involved. Thus, according to the method disclosed in Japanese Laid-open Patent Publication No. 2012-44421, in a condition in which it is necessary to perform real-time processing for the purpose of calculating the data value for a preview image (i.e., in a condition in which it is necessary to perform processing in a short period of time), the processing load is large.
During the calculation of specular colors in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, a normal vector (N) indicating the normal direction of the object surface, a light source vector (L) indicating the direction of the light source, an eye direction vector (E), and a parameter (n) indicating the degree of diffusion of the gloss are used; and the specular colors are determined according to a predetermined calculation formula. Moreover, from the (post-dynamic-range-compression) values of specular colors calculated in the abovementioned manner, a synthesis ratio (α) of specular colors and a synthesis ratio (β) of diffuse reflection are calculated according to predetermined calculation formulae.
However, in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, the configuration is such that the parameter (n) indicating the degree of diffusion of the gloss is measured for each patch in an actually-output patch image and is stored in an LUT. Since the parameter (n) indicating the degree of diffusion of the gloss needs to be measured for each patch image, an enormous number of man-hours are taken to create the LUT. Moreover, also at the time of calculating the specular colors using the LUT created in the abovementioned manner, it becomes necessary to search for the concerned location from the enormous LUT, thereby resulting in an increase in the processing load.
Moreover, in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, during the process of calculating the specular colors, it is also necessary to calculate the angular difference between the light source vector (L) and the reflection vector (R) of the eye vector. Since such calculation of the angular difference needs to be performed at each position on the object, the calculation load goes no increasing. If the light source is a point light source or a line light source, then a small amount of calculation is required to calculate the angular differences. However, if a plurality of light sources is present and has a complex shape, many calculations are required to calculate the angular difference between the light source and the reflection vector at each position on the object. Hence, the angular differences cannot be calculated in a simple manner. Thus, it is not possible to deal with a case in which a plurality of light sources having complex shapes is present.
Furthermore, in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, trouble occurs at the location of calculating the synthesis ratio between the specular reflection and the diffuse reflection. In the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, at the time of calculating the synthesis ratio, it is necessary to first calculate a maximum value Cs'(max) of the (post-compression) specular colors. At that time, it is a feature of the maximum value Cs'(max) of the (post-compression) specular colors that, only after a (post-compression) specular color Cs' is calculated for all points on the object, the maximum value Cs′ becomes clear for the first time. Hence, in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-246049, the (post-compression) specular color Cs′ is calculated for all points on the object and then the maximum value Cs′(max) of the (post-compression) specular colors is determined. Subsequently, from the maximum value Cs′(max) of the (post-compression) specular colors and from the (post-compression) specular color Cs′, the synthesis ratio between the specular reflection and the diffuse reflection is determined for all points on the object followed by the determination of the reflected color. That is, for all points on the object, the data access needs to be performed twice, which leads to an increase in the calculation load.
In the technology disclosed in Japanese Laid-open Patent Publication No. 2010-152533, texture information data can be obtained using a texture profile. Moreover, the texture information data is expressed using parameters of the bidirectional reflectance distribution function (BRDF); and is expressed as a coefficient (m) indicating the surface roughness of the object, an object surface reflectance (ρs), a coefficient (ks) corresponding to the object surface reflectance (ρs), an internal diffuse reflectance (ρd) of the object, a coefficient (kd) corresponding to the internal diffuse reflectance (ρd) of the object, and an index of refraction (n) of the object.
In the technology disclosed in Japanese Laid-open Patent Publication No. 2010-152533, in the case of performing a printed material preview, the value of data for preview display is calculated using the abovementioned parameters and implementing a calculation formula specified in Japanese Laid-open Patent Publication No. 2010-152533. However, such calculation needs to be performed at each position of the printed material to be previewed. As a result, the calculation load becomes extremely large.
Besides, regarding obtaining the parameters of the bidirectional reflectance distribution function (BRDF) too, the incident light and the reflected light need to be varied independent of each other. Hence, obtaining the parameters also requires a lot of time and effort. Moreover, every time a print image formed on a new paper sheet is to be reproduced using a preview device, it becomes necessary to obtain the BRDF parameters. Hence, in the technology disclosed in Japanese Laid-open Patent Publication No. 2010-152533, since the method of obtaining the parameters requires a lot of time and effort, reproducing a preview of a print image formed on a new paper sheet requires a lot of toil. Thus, it becomes difficult to deal with print images formed on various types of paper.
Therefore, there is a need for an image processing device and an image processing method that, in regard to a three-dimensional display preview function, enable achieving enhancement in the texture including the gloss feel of the printed material and enable displaying (reproducing) the texture.